Blasting arrangement for oil shale mining



@7511 (JP 394% 90% SEAWH' BOOM Sept. 9, 1969 G. R. HAWORTH ET AL 3 6,

BLASTING ARRANGEMENT FOR OIL SHALE MINING Filed Feb. 5, 1968 2Sheets-Sheet 1 f 0 FIG. 2 1

42" 43" 44" 45" 46" 3o o o D 0 Q 0 o 0 a o 9% JV T F l 40 3/0 4 FIG. 3

GORDON R. HAWORTH PETER G. ZAMBAS INVENTORS ATTORNEY Sept. 9, 1969 G. R.HAWORTH ET AL 94 BLASTING ARRANGEMENT FOR OIL SHALE MINING Filed Feb. 5,1968 2 Sheets-Sheet 2 ,coooooooo o o o O O 5 o o o i 5a 59 60 5 0 50d oo o are 592! l we 50c 1 55 GORDON R. HAWORTH PETER G. ZAMBAS INVENTORSwap/aw ATTORNEY United States Patent O US. Cl. 29913 14 Claims ABSTRACTOF THE DISCLOSURE This specification discloses a blasting technique foruse in excavation of an oil shale deposit during the subterranean miningthereof. Primary blasting holes are provided in a Working zone such as aheading or bench within the mine. In addition, a row of explosive-loadedsecondary blasting holes is provided along a line between the workingzone and a support zone adjacent the Working zone. Thus, in a benchinground, secondary holes extend downwardly through the bench from the topthereof and in a heating round the secondary holes extend into theheading from the heading face. The secondary and primary blasting holesare detonated in a desired sequence. Preferably, the secondary blastingholes are detonated first although this sequence of operation may bereversed. The secondary blasting holes carry a lower explosive chargethan the primary holes and also are spaced closer together than theprimary holes.

BACKGROUND OF THE INVENTION This invention relates to the subterraneanmining of oil shale and more particularly to the blasting of oil shaledeposits in carrying out mining operations.

Large deposits of oil shale are located beneath the earths surface inflat-lying subterranean formations. One technique for recovering the oilfrom such deposits involves the application of underground miningprocedures by which the oil shale is removed from its naturalsubterranean location to the surface of the earth. At the surface theoil shale is crushed as necessary and then subjected to retorting. Theshale oil recovered during such retorting operations then may besubjected to further refining operations in order to produce desirablehydrocarbon products such as gasoline.

In the underground mining procedures used, the extraction of the oilshale from its subterranean location requires, as a practical matter,the excavation of large stopes in order to accommodate the mechanicalequipment used. For example, in the room and pillar mining technique foroil shale, it is desirable to provide open stopes or rooms which exhibitat least horizontal dimension on the order of sixty feet and height ofabout forty to one hundred feet. In forming stopes of such size theblasting of large quantities of shale in single rounds is an economicnecessity. The large blasting rounds involved induce high magnitudevibrations in the mine, particularly in the pillars adjacent the workingzones of the mine in which blasting operations are carried out.

Oil shalenormally has a laminated structure which exhibits a largenumber of joints and incipient planes of weakness. These characteristicsof the oil shale, in combination with the high magnitude of vibrationsncountered during blasting operations, often result in a generalweakening of the pillar structures adjacent the blasting areas and alsoin the excessive amounts of spallation in the sides or ribs of thepillars. These conditions create severe safety hazards. For example, thepillars may become so weakened that they fail to support "ice adequatelythe roof of the mine with the attendant result that cave-ins may occur.In addition, the vibrations transmitted to the pillars are in turntransmitted to the roof of the mine, and this may result in weakening ofthe portion itself. Thus, even though the pillars may be of sufficientstrength to support the mine, portions of oil shale may become partedfrom the roof and fall into the open stopes with the attendant hazard topersonnel Working in the mine.

SUMMARY OF THE INVENTION In accordance with the present invention, thereis provided a new and improved blasting technique for use in thesubterranean mining of an oil shale deposit. In earring out theinvention a plurality of explosive-loaded primary blasting holes areprovided in a working zone of the oil shale deposit within the mine. Inaddition, a plurality of explosive-loaded secondary blasting holes areprovided along a line between the working zone and a support zoneadjacent the working zone. The secondary blasting holes have a loweraverage explosive charge than the primary holes and function to controlthe effect of the primary blasts in order to minimize damage to thesupport zone. The primary and secondary blasting holes then aredetonated in the desired sequence. The secondary blasting holespreferably are detonated prior to detonation of the primary blastingholes. In a preferred embodiment of the invention, the average spacingof the secondary blasting holes is less than the average spacing of theprimary blasting holes.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is an isometric view, withparts broken away of a subterranean oil shale mine being developed bythe room and pillar method;

FIGURE 2 is an illustration, partly in section, showing the applicationof the present invention in blasting a heading round;

FIGURE 3 is a sectional view taken along line 3--3 of FIGURE 2;

FIGURE 4 is an illustration, partly in section, showing the applicationof the invention in the blasting of a benching round; and

FIGURE 5 is a sectional view taken along line 55 FIGURE 4.

DESCRIPTION OF SPECIFIC EMBODIMENTS With reference to FIGURE 1 of thedrawing, there is illustrated a subterranean oil shale deposit 10 whichis being mined by the room and pillar procedure. The oil shale depositlies between formations 12 and 14, and above formation 14 additionaloverburden 16 extends to the surface 17 of the earth. As illustrated,the mine comprises a number of stopes such as those indicated byreference numerals 19, 20, and 21. The stopes are formed in the oilshale deposit by suitable excavation procedures and leave supportstructures, commonly termed pillars, which extend between the floor ofthe mine and the roof thereof in order to support the overburden abovethe mine. The pillars may be substantially continuous, such as thepillar indicated by reference numeral 23, although more typically theywill be in block form such as those indicated by reference numerals 24and 25.

Excavation of the stopes within the mine typically is accomplishedthrough the application of heading and benching blasting techniques. Byway of example, the stope 20 shown in FIGURE 1 may be extended by fullheading blasting in which a number of blasting holes are drilled intothe face 26 of the heading and then loaded With explosives anddetonated. Further excavation of the stope 19 may be effected by headingblasting through the similar utilization of blasting holes in face 27 orby a bench blasting procedure in which a plurality of substantiallyvertical holes are drilled into the bench 28 from the top thereof,loaded, and then detonated.

The invention will now be described in detail with reference to itsapplication in the blasting of a heading round. With reference toFIGURES 2 and 3, there is illustrated a heading face 30 at the end of astope 31. For example, the face 30 may be considered to correspond tothe heading face 26 shown in FIGURE 1. The stope 31 is defined by theribs 34a and 35a of pillars 34 and 35, the heading floor 31a, and theroof 31b. The portion of the unworked oil shale which is to be excavatedby the blasting procedure to provide an extension of stope 31 is termedthe working zone and is indicated generally by bracket 36. The portionsadjacent the working zone which are to be left in place to becomeextensions of pillars 34 and 35 are designated by brackets 37 and 38,respectively, and are termed the support zones.

In carrying out the invention, rows 40 and 41 of secondar blasting holesare drilled into the heading from the face 30. The holes desirably arelocated as close to the lines of the ribs 34a and 35a as possible andlie in a common plane. The secondary blasting holes may be drilled toany suitable diameter and spacing. Typically, the holes will be on theorder of about four inches in diameter and will be spaced approximatelyfour feet apart. In addition to the secondary blasting holes whichprovide for blasting control, the heading also is provided with aplurality of primary blasting holes such as those indicated by referencenumerals 42-46. As is best shown in FIGURE 3, the primary holes in theheading round are drilled in accordance with a V-cut procedure in orderto notch the heading face to provide for an adequate free face for theblasting procedure.

The primary and secondary holes are loaded such that the primary holeshave a greater average explosive charge than the secondary holes. By wayof example, each of the primary holes may be loaded with five pounds perfoot of a suitable explosive agent such as semi-gelatin powder, with thefirst ten feet of hole either vacant or filled with stemming. Thus, aprimary hole drilled to a depth of twenty-five feet may be loaded withapproximately seventy-five pounds of explosive. The secondary holesnormally will be loaded with an explosive charge of approximatelyone-fifth or less of the power of the primary loads. For example, wherethe primary holes are loaded as described above, each of the secondaryholes may be loaded with strings of powder made from l-grain primacordand one and one-half-inch by eight inch sticks of semi-gelatin powder.The semi-gelatin powder is taped to the primacord with twenty-inch gapsbetween adjacent sticks.

After loading the respective blasting holes they are detonated in thedesired sequence. Preferably, the secondary blasting holes are detonatedfirst in order to effect a pre-splitting function with regard to theprimary blasting round. The effect of this is to form fractures alongthe planes in which the secondary holes lie which tend to de-couple thesupport zones 37 and 38 of the oil shale deposit from the working zone36. Thus, the vibrations induced by the blasting of the primary roundsare transmitted to the support zones at greatly reduced intensity. Inaddition, the resulting walls or ribs of the pillars resulting from theheading round are relatively smooth and resistant to spalling.

After detonation of the secondary holes the primary blasting holes aredetonated in order to remove oil shale from the working zone 36. By Wayof illustration, the primary and secondary blasting holes shown inFIGURE 2 can be detonated in the following sequence. The secondary holespreferably are detonated in groups of three or more. For example, theholes in rows 40 and 41 may be detonated in groups of three at intervalsof 25 milliseconds. Thus, the three lower holes in row 40 may bedetonated at zero milliseconds and the progression repeated until theupper three holes in row 41 are detonated at milliseconds. Thereafter,the primary holes 43-43" and 44-44 are detonated at 200 milliseconds,holes 42- 42" and 4-5-45" at 250 milliseconds, and holes 46-46" at 300milliseconds. The holes along the top and bottom of the heading face aredetonated at 350 to 400 milliseconds.

While it usually will be desirable to detonate the pri mary andsecondary blasting holes in a common round through the use of electricaldetonating equipment, it will be recognized that the secondary holes maybe drilled, loaded, and detonated before drilling of the primary holes.

It is preferred in carrying out the invention that the spacing betweenthe secondary blasting holes be less on an average than the spacingbetween the primary blasting holes. In this regard, the nature of oilshale is such that blasting can be carried out most economically andexpeditiously by utilizing heavily loaded, widely spaced, primary holes.The secondary holes on the other hand should be located in a relativelyclosely spaced pattern in order to obtain effective de-coupling. Itusually will be desirable to provide an average spacing betweensecondary holes of less than one-half of the average spacing betweenprimary holes. It also is preferred that the outer perimeter primaryholes, e.g., holes 42, 42, 46, etc., be located relatively close to theadjacent row of secondary holes. More particularly, the distance betweenthe outer perimeter primary holes and the line along which the adjacentsecondary holes lie normally should be less than the average distancebetween primary blasting holes and also less than twice the spacing ofthe secondary holes. Thus, the dimension of D in FIGURE 2 should be lessthan the average spacing of the primary blasting holes and less thantwice the spacing of the secondary blasting holes in row 40.

In addition to the above criteria, it is preferred that the secondaryblasting holes extend further into the oil shale deposit from the face30 than the primary holes. This relationship should be observed in orderto clearly delineate the working and support zones and produce thedesired de-coupling action.

Turning now to FIGURES 4 and 5, there is illustrated the use of theinvention in blasting benching rounds. This procedure is similar to thatdescribed above with reference to the blasting of heading rounds exceptthat in this case the secondary holes are drilled downwardly through abench. More particularly, and with reference to FIGURES 4 and 5, thereare provided rows 50 and 52 of secondary blasting holes located alongeach side of a bench 54 and as close as possible to the ribs of adjacentpillars 55 and 56. The secondary holes extend downwardly through thebench 54 and may be drilled vertically as shown in FIG- URE 5 orinclined. A plurality of primary blasting holes, such as those indicatedby reference numerals 58, 59, 60, and 61 are drilled into the bench 54between the rows 50 and 52 of secondary holes. The secondary and primaryblasting holes are loaded with explosives similarly as described abovewith reference to FIGURES 3 and 4. Thus, the average explosive charge ofthe secondary holes is less than the average explosive charge of theprimary holes, preferably by a factor of at least one-fifth. Afterdrilling and loading of the blasting holes they are detonated in thedesired sequence with the secondary holes being detonated first ingroups of three or more. After detonation of the secondary holes, theprimary holes are detonated in a desired sequence with those next to thefree face normally being detonated first.

The relationships between the primary and secondary blasting holespreferably are the same as those described above with reference toFIGURES 3 and 4. Thus, the average spacing between the primary blastingholes located between rows 50 and 52 preferably is greater than theaverage spacing between the secondary blasting holes. In addition,theouter perimeter primary blasting holes, such as those indicated byreference numerals 59 and 61, preferably are located from rows 50 and 52by a distance less than the average distance between the primaryblasting holes and also less than twice the spacing between thesecondary blasting holes. It also is desirable that the secondaryblasting holes in rows 50 and 52 extend into the oil shale deposit fromthe top of bench 54 by a distance greater than the primary blastingholes. Thus, as is shown in FIGURE 5, the primary blasting holes 58 and60 extend from the top of the bench and terminate in the bench atapproximately the level of the bench floor 62. The secondary blastingholes 50a50d extend further into the oil shale deposit and terminate ata level below the floor of the bench.

In the procedures heretofore described, the secondary blasting holes arefired prior to detonation of the primary blasting holes. While thissequence of operation normally will be preferred in order to provide foreffective decoupling as described above, it sometimes may be desirableto reverse this order of operation. Thus, in either benching or headingblasting operations, the primary blasting holes may be drilled, loaded,and fired, after which the secondary blasting holes may be detonated. Inthis case the primary blasting holes should be located such that thewidth of the burden left in place after firing of the primary round isless than the spacing between the secondary blasting holes. Statedotherwise, the distance between the face exposed by the primary blastinground and the row of secondary blasting holes should be less than thedistance between such holes.

What is claimed is:

'1. In the working of an oil shale deposit by means of a subterraneanmine therein having stopes in said deposit.

and pillars which support the overburden over saidmine, the method ofblasting within said mine comprising:

(a) providing a plurality of explosive-loaded primary blasting holeswithin a working zone of said oil shale deposit;

(b) providing a plurality of explosive-loaded secondary blasting holesalong a line between said working zone and a support zone of saiddeposit adjacent said working zone, said secondary holes having a loweraverage explosive charge than said primary holes; and

-(c) detonating said blasting holes.

2. The method of claim 1 wherein the average explosive charge of saidsecondary holes is less than one-fifth the average explosive charge ofsaid primary holes.

3. The method of claim 1 wherein the average spacing of said secondaryblasting holes is less than the average spacing of said primary holes.

4. The method of claim 1 wherein the average spacing of said secondaryblasting holes is less than one-half the average spacing of said primaryholes.

5. The method of claim 1 wherein said primary blasting holes aredetonated prior to said secondary blasting holes to leave a burden of awidth less than the average spacing between said secondary holes, andthereafter detonating said secondary holes.

6. The method of claim 1 wherein said primary blasting holes aredetonated subsequent to said secondary blasting holes.

7. The method of claim 6 wherein said secondary holes extend into saiddeposit to a depth greater than said primary holes.

8. The method of claim 6 wherein the primary blasting holes nextadjacent said line of secondary blasting holes are spaced from said lineby a distance less than the average spacing of said primary holes andless than twice the average spacing of said secondary holes.

9. In the working of an oil shale deposit by means of a subterraneanmine therein having stopes in said deposit and pillars which support theoverburden over said mine, the method of blasting a heading within saidmine comprising:

(a) a long each side of the face of said heading providing a row ofexplosive-loaded secondary blasting holes extending into said headingfrom the face thereof;

(b) providing a plurality'of explosive-loaded primary blasting holes insaid heading located between said rows of secondary holes, said primaryholes having a greater average explosive charge and a greater averagespacing than said secondary holes;

(c) detonating said secondary blasting holes; and

' (d) subsequent to step (c) detonating said primary blasting holes.

10. The method of claim 9 wherein the average explosive charge of saidsecondary holes is less than one-fifth the average explosive charge ofsaid primary holes.

-11. The method of claim 10 wherein said secondary holes extend intosaid heading from the face thereof by a distance greater than saidprimary holes.

12. In the working of an oil shale deposit by means of a subterraneanmine therein having stopes in said deposit and pil ars which support theoverburden over said mine, the method of blasting a bench Within saidmine comprising:

(a) along each side of said bench providing a row of explosive-loadedsecondary blasting holes extending downwardly into said bench from thetop thereof;

(b) providing a plurality of explosive-loaded primary blasting holes insaid bench located between said rows of secondary blasting holes, saidprimary holes having a greater average explosive charge and a greateraverage spacing than "said secondary holes;

(c) detonating said secondary blasting holes; and

(d) subsequent to step (c) detonating said primary blasting holes.

13. The method of claim 12 wherein the average explosive charge of saidsecondary holes is less than one-fifth the average explosive charge ofsaid primary holes.

14. The method of claim '13 wherein said secondary holes extenddownwardly through said bench by a distance greater than said primaryholes.

References Cited UNITED STATES PATENTS 1,269,747 6/1918 Rogers 299-21,833,368 11/1931 ORourke 299-13 1,919,636 7/ 1933 Karrick 299-2 FOREIGNPATENTS 163,027 9/ 1948 Austria.

OTHER REFERENCES How & Why Mines Go To Smoothwall, Engineering & MiningJournal, vol. 166, No. 10 October 1965, pp. 92- 95.

Culver, Dr. R. S., Pre-Split Blasting, The Mines Magazine, March 1966,pp. 2024.

E. I. du Pont de Nemours & 00., Four Major Methods of ControlledBlasting, Pamphlet No. Ex-1l79-A, rev. 4-64.

ERNEST R. PURSER, Primary Examiner U.S. Cl. X.R. 102-23; 299-11

